Background of the Art
Initially, resists were applied to substrates in liquid form. The resist was imagewise subjected to radiation to form relatively soluble and relatively insoluble areas. Upon treatment with an appropriate developer solution, the relatively soluble areas were removed and a physical mask in the desired image pattern was left on the surface of the substrate. The exposed area of the substrate would then be treated by either deposition of material onto the exposed areas (e.g., metal deposition by vapor coating or electrolytic processes) or etching of the surface of the substrate in the area exposed through the mask.
One of the first advances in the use of dry-film photoresist materials was discussed in U.S. Pat. No. 3,469,982 in which a laminable negative-acting single layer film was adhered to a substrate and used as a photoresist.
U.S. Pat. No. 4,193,797 discloses the use of single layer laminable films of positive-acting dry-film photoresist compositions for use in photoresist processes.
U.S. Pat. No. 4,349,620 teaches multi-layer photosensitive film resists (positive and negative) consisting of a plurality of layers having different properties. Particularly disclosed is a carrier sheet, an adjacent first photosensitive layer, and a second photosensitive layer having different adhesion properties from the first layer.
Particular requirements in the positive-acting photoresist art have lead to the use of two layer or multilayer laminable sheets or coatings of photoresist materials in order to improve the sensitometric or physical properties of the dry-film resist. U.K. patent No. 1,493,833 shows the use of a photoresist comprising a carrier layer, a photosensitive layer (including positive-acting photosensitive layers) and a thermoplastic non-photosensitive layer which is soluble in aqueous or organic solvents. A host of natural and synthetic polymers are disclosed for these non-photosensitive layers. U.S. Pat. No. 4,204,009 discloses the use of a positive-acting resist having two photosensitive layers of different reactivities adjacent each other on top of the substrate to be treated. U.S. Pat. No. 4,217,407 discloses the use of multiple layer positive-acting resist materials which comprise an o-quinone diazide containing layer in combination with at least one other layer which is permeable, swellable, or soluble by alkaline envelopers. A brief list of non-photosensitive compositions is provided.